1. Field of the Invention
The present invention relates to a high-frequency module including a plurality of filter devices.
2. Description of the Related Art
A mobile apparatus and the like having a wireless communication function includes a filter circuit for passing a high-frequency signal with a desired frequency and attenuating high-frequency signals having frequencies other than the desired frequency.
For example, Japanese Unexamined Patent Application Publication No. 2012-109818 discloses a filter circuit including a plurality of resonators. Specifically, in the filter circuit of Japanese Unexamined Patent Application Publication No. 2012-109818, a plurality of resonators are connected in series between an input terminal and an output terminal.
In the configuration disclosed in Japanese Unexamined Patent Application Publication No. 2012-109818, a path (hereinafter, called a compensation circuit) including an inductor or an inductor and a capacitor is connected in parallel with the filter circuit to improve attenuation characteristics outside of a pass band. The compensation circuit is adjusted such that a suppression signal propagating through the compensation circuit has the same amplitude as a high-frequency signal (suppression-target signal) outside of the pass band passing through the filter circuit and has a phase opposite to that of the high-frequency signal. As a result, the suppression-target signals cancel each other out at a connection node between the filter circuit and the compensation circuit and are not output from the output terminal.
However, with the above-described configuration in a high-frequency module, the compensation circuit is provided outside of the filter circuit, thus causing an increase in the size of the module.
Further, the outside of the filter circuit is likely to be influenced by the external environment. Specifically, the compensation circuit, which is likely to be influenced by noise outside of the filter circuit, is likely to couple with other circuits. Further, the compensation circuit is likely to be influenced by coupling between mounted devices outside of the filter circuit. As a result, the high-frequency module will have variations in the characteristics, whereby it becomes difficult to make the attenuation characteristics be desired characteristics.